Development of In‐Office Laryngeal Nerve Conduction Studies: Computed Tomography and Cadaveric Study

Abstract

In-office recurrent laryngeal nerve conduction studies (NCSs) are a technique that can potentially provide information about laryngeal innervation. NCS is essential in the management of other neuropathies including carpal tunnel syndrome and spinal cord injury. We hypothesize that laryngeal NCS may have similar utility in managing patients with vocal fold paralysis, atrophy, and neurodegenerative disease. NCSs are technically challenging because they require transcervical stimulation of the recurrent laryngeal nerve (RLN). This study combines radiographic data with cadaveric dissection to describe the anatomic parameters for optimal RLN stimulation.Study Design: Radiographic and Cadaveric Study. Methods: Fifty computed tomography scans were reviewed to determine the dimensions for ideal needle electrode placement. These values were compared to measurements from 12 fresh human cadaveric neck dissections. Ultrasound imaging was utilized in select cases. The neck was dissected to assess the accuracy of electrode placement.Results: Radiographically, the mean transcervical depth to the RLN was 33.2 mm AE 8.3 mm in males versus 29.4 mm AE 9.4 mm in females. The working space between the lateral trachea and carotid artery was 15.3 mm AE 3.6 mm on the right and 14.1 mm AE 2.9 mm on the left. After placement of stimulating electrodes into the cadaveric neck, the electrode tips were consistently within 8 mm of the RLN. Ultrasound guidance improved placement accuracy of the stimulating electrode.Conclusions: Laryngeal NCSs can provide detailed and objective information about laryngeal innervation that could dramatically improve the management of various neuropathies. In-office NCSs require technical precision, and this study describes anatomic factors that may affect the feasibility of performing this technique.

Recurrent laryngeal motor nerve conduction studies in a rat model: Establishing an objective measure for investigating laryngeal innervation

“…However, the variability and uncertainty in the location of the stimulus prevented clinically useful comparisons of outcome metrics, especially nerve conduction study measures such as the latency to CMAP onset. Bhatt et al utilized cadaveric dissection, CT imaging, and ultrasound guidance to delineate the key landmarks and parameters that can be used to guide consistent transcutaneous stimulation of the RLN 21 . Others have attempted use of multielectrode array stimulation and transcranial magnetic stimulation to produce more consistent stimulation 19,20 .…”

“…Bhatt et al utilized cadaveric dissection, CT imaging, and ultrasound guidance to delineate the key landmarks and parameters that can be used to guide consistent transcutaneous stimulation of the RLN. 21 Others have attempted use of multielectrode array stimulation and transcranial magnetic stimulation to produce more consistent stimulation. 19,20 Perhaps by combining key anatomical landmarks, image guidance, and multiple stimulation paradigms and locations, consistent and clinically valuable data, including comparable measures of nerve conduction velocity, may be obtained.…”

“…Neuromuscular disease and aging have been shown to negatively affect the CMAP in the arm, 13 hand, 14 and leg muscles, 15 and are associated with poorer muscle function 16–18 . Prior studies have attempted to perform MNCS in the larynx but have had limited clinical or experimental utility 19–21 …”

“…[16][17][18] Prior studies have attempted to perform MNCS in the larynx but have had limited clinical or experimental utility. [19][20][21] The goal of this study was to explore the feasibility of performing recurrent laryngeal motor nerve conduction studies (rlMNCS) in the rat larynx. We hypothesize that application of rlMNCS in an in-vivo model may be useful for study of the neuromuscular changes that occur in the diseased or aging larynx and will provide a basis for prevention and treatment of diseases affecting laryngeal neurophysiology.…”